Electric detonator



April 25, 1951 R. H. F. sTREsAU 2,981,186

ELECTRIC DETONATOR Filed Sept. 15, 1954 INVENTOR R. H. E STRESAU BY (MQ. A'FTQRNES 2,981,186 Patented Apr. 25, 1961 hee ELECTRIC DETONATOR Richard H. F. Stresau, Washington Grove, Md., assigner to the United States of America as represented by the *SecretaryY of the Navy Filed sept. 1s, 19154, ser. No. 456,342 111 claims. (C1. we zs) (Granted underv Title 3'5, U.S. Code (1952), sec. 266) The invention described herein may be manufactured and used by or for the Government of the United States of America for governmental purposes without the payment of any royalties thereon or therefor.

This invention relates t-o electrical detonating devices and 'more particularly to an improved electrical detonating device containing no primary explosive and having lan exceedingly low explosive energy requirement for initiating lan explosion in an otherwise relatively insensitive high explosive material.

"The term primary explosive as employed herein is definedy as an explosive having the characteristics of that class of explosives of Vwhich mercury fulminate and Vlead azide are Well known examples; and the term high explosive herein is defined in accordance lwith its regular accepted meaning as an explosive having the characteristics of tha-t class of explosives known in the art as high explosives, tetryl, TNT, and pentaerythn'tol tetranitrate being well known examples.

The prior art electric detonating devices having a relatively insensitive high explosive base detonator charge, such as tetryl or pentaerythritol tetranitrate, employ an ignition mixture containing a highly sensitive primary explosive, such as fulminate of mercury or lead azide, to initiate detonation of a less sensitive detonator base charge. When these prior art detonators are used in military weapons, safety considerations require that the detonator, or the primary explosive charge thereof, be separated from the main high explosive charge of the bomb, projectile, or other device with which the detonator is assembled, by a mechanical arming mechanism which operates to align the detonator or primary explosive with the high explosive only after launching of the weapon. Such an arrangement is well known and disclosed, flor example, in Patent No. 2,511,872 to L. L. Parker, issued June 20, 1950.

These arming mechanisms often present design problems of considerable difficulty where space and weight factors are critical in the particular military application, such asin a projectile fuze, and it has frequently been proposed that electrical detonators be rendered safe b-y isolating or shorting the detonator leads and eliminate a mechanical arming means. However, this proposal is objectionable since it does not meet the fundamental safety requirement that primary explosives lbe separated from other components of the explosive system until the device vis launched.

The detonator described herein is intended for use in fuzes and other ordnance initiating devices where safety considerations require that the primary explosive initiating charge vbe separated from the high explosive main charge of the particular military device, and where space or weight factors are critical, presenting difficult design problems unless the mechanical arming mechanism is eliminated. In accordance with the present invention,

an'elect-rical detonator is described containing no primary explosive, thus eliminating the need for a mechanlcal aiming mechanism.

It is an important object of the invention, therefore, to provide an electrical detonator of the type described which contains no primary explosive.

Another object of this invention is to provide an electrical detonator having exceedingly low initiatingenergy requirements for initiating an explosive in an otherwise insensitive material. f t

A further object of this invention is to provide an electrical detonator having a novel arrangement, Vcombination, and construction of elements', and wherein the constituents of the charges are so selected and arranged that the detonator will be positive in operation, substantially immune to premature explosions, simple to assemble, and Iinexpensive to manufacture.

A still further object of this invention is to provide an electrical detonator for use in a military weapon which will meet safety requirements by using only electrical safety devices, thus eliminating the need for a conventional mechanical arming mechanism.

Other objects and many of the attendant advantages of this invention will become apparent to those skilled in the art by reference to the following detailed description of a preferred embodiment thereon, when considered in connection with the accompanying drawing, in which:

Fig. l is a greatly enlarged view in longitudinal section of al1-electrical detonator constructed'in accordance with the present invention; and

Fig. 2 is a detailed sectional plan view taken'generally along line 2 2 of Fig. 1,`withV a part thereof broken away.

Referring now to the drawing, and more particularly to Fig. 1, the electrical detonator of this invention generally designated as 1 comprises a metallic cylindrical casing 3, preferably of brass, having an acoustical impedance of higher value than the acoustical impedance of the explosive material disposed therein and a bore 4 open at the upper end and terminating at the lower end into a stepped bore 5 forming an annular shoulder 6. The metallic casing 3 is provided with an annular opening 8 in the lower end thereof for permitting a pair of ele'ctrodes 9 to protrude therethrough for establishing an electrical connection, the diameter of the annular opening being suicient to provide a spacing between the -electrodes 9 and between each of the electrodes 9 and metallic casing 3. Y Y

A rst solid cylindrical plug 7, which may be molded of glass, or other suitable hard dielectric materialfsuch as a ceramic material, comfortably ts in bore 4 and rests on shoulder 6. The plug 7 has a pair of electrodes 9 preferably provided with deformed portions 16 molded therein, extending from the lower end thereof a suitable distance and terminating at the upper surface in two semicircular layers of spray metal 11 respectively connected to each of the electrodes 9 and separated by a diametrically arranged slot 112 in the spray metal about .03() inch in width. The spray metal 11 may lbe silver solder, or other suitable metal and is preferably applied about .005 inch in depth bywell known methods to the upper surface of plug 7 and does not extend quite to the outer cylindrical contour of the plug 7 so as to avoid short circuiting the electrodes 9.l This arrangement provides a slot 12 about .030 inch in width by .005 inch in depth which is lled -with a iinely divided explosive powder 18 such as powdered pentaerythritol tetranitrate, or other suitable relatively insensitive high explosive, the powdered explosive 18 serving as an ignition charge. A bridge wire 14 of tungsten or other suitable material, best shown in Fig. 2 in which a portion of the spray metal and explosive powder 18 has lbeen removed for purpose of illustration, is connected to electrodes 9 by the spray metal 11 and extends across slot 12, the bridge wire lbeing in intimate contact with powdered explosive 18 disposed therein.

The ignition assembly, generally designated 10, comprising the plug 7, electrodes 9 with deformed portions 16, semi-circular layers of spray metal 11, slot 12 filled with the ignition charge of powdered high explosive 18, and bridge wire 14, may be conveniently assembled as a unit and inserted through the'upper end of bore 4 into position against shoulder 6. i

A second solid cylindrical plug 15, likewise of glass, or other suitable hard dielectric material, havinga diameter slightly less than bore 4, is disposed concentrically with respect to metallic casing 3 and above first plug 7 `abutting the spray metal semicircles 1l and the ignition charge of powdered high explosive 18 disposed in slot V12, thereby forming an annular recess 17 between second plug 15 and bore 4 which is in communication with slot 12. An intermediate explosive 19, such as trinitroethyl trinitrobutyrate, or other suitable easily cast relatively insensitive high explosive, is placed in bore 4,.a sufcient quantity being used to fill annular lrecess 17` and to form a layer over the top of second plug 15, and the entire assembly heated just sufficiently to cast intermediate explosive 19 in place, thereby forming an explosive cast covering the top of second plug 15 and extending therefrom as a thin cylindrical wall down wardly between the plug 15 and bore 4Vinto intimate contact with the outer ends` of slot 12 and the ignition charge of powdered high explosive 18.

VA base explosive 20, such as pentaerythritol tetra nitrate or other suitable relatively insensitive high explosive, is disposed in several increments, two being shown, above second plug 15 and in abutting relation with the layer of 'intermediate explosive 19 covering second plug 15. Base explosive is then solidified by applying a pressure of about 10,000 pounds per square inch thereto, thereby not only firmly pressing base explosive 20 into intimate contact with intermediate explosive 19, but causing all elements disposed within metallic casing 3 to be consolidated and remain under considerable static pressure in the completed detonator.

Thus, in accordance lwith this invention and as specifically described With reference herein to a preferred ernbodiment thereof, electric detonators have been produced that contain no primary explosive, that meet safety requirements when used in a fuze with only an electrical safety device, that have exceedingly small explosive energy requirements for initiating-an explosion in a relatively insensitive material, and that have novel arrangement, combination, and construction of the elements thereof.

From the foregoing description, it is apparent that when the bridge wire 14 is energized to incandescence in response to a minute electric current passing therethrough, the thin layer of finely powdered high explosive 18 disposed in slot 12 and confined between plugs 7 and 15, `will be ignited. The flame or flash produced by ignition of the minute quantity of powdered explosive 18, in combination with the intensifying effect of confinement in slot 12 and between the hard surfaces of plugs 7 and 15 whereby the reaction products are restrainedfrom dispersing except along slot 12, produces sufficient heat and pressure by reason of this close confinement to effectively initiate detonation of the relatively insensitive intermediate high explosive 19 disposed in narrow annular recess 17, which is in communication with slot 12. The detonation of the small quantity of intermediate explosive 19, taken with the intensifying effect of confinement between plug 15 metallic casing 3, and highly compressed base charge v20 whereby the reaction products are restrained from dispersing except along narrow annular recess 17, produces sufficient power by reason of the high degree of heat and pressure generated therein to propagate the explosion and cause base explosive 20 in communication therewith to detonate.

It is understood that the dimensions, configuration, and composition of the various elements comprising the detonator of this invention may be varied without departing from the spirit and scope of the present invention. However, a specific embodiment thereof may use a brass casing 3 about l inch in length and 1/2 inch outside diameter with a .221 inch bore 4 extending to within about 1A; inch of the lower end. Theignition assembly 10 may comprise a glass plug 7 about 1A inch in length and .210 inch in diameter having apairfof tinplated brass electrodes 9 embedded therein and extending a suitable distance from the lower end, with each electrode terminating at the upper or inner surface in a semicircular layer of silver solder spray metal 11 about .005 inch in depth. The spray metal segments 11 do not extend quite to the outer cylindrical contour of plug 7 to avoid short circuiting electrodes 9 when the assembly is inserted in metallic casing 3, and are separated about .030 inch, thereby forming a diametrically arranged slot .030 inch in width, and .005 inch in depth. A bridge wire of tungsten having a diameter of .001 to .0002 is connected to electrodes 9 and extends across slot 12, being in intimate contact with finely powdered relatively insensitive ignition charge of high explosive 18, which may be pentaerythritol tetranitrate, disposed therein. The powdered explosive 18 may be prepared lby milling 24 hours in chloroform, and only about .001 gram is suicient to fill slot 12 and initiate detonation of relatively insensitive cast :intermediate high explosive 19. Plug 15 may be of glass about 1A inch in length and 3A0 inch in diameter and when in place the plug forms a narrow annular recess 17 with metallic casing 3 which is filled with an easily cast relatively insensitive high explosive such as trinitroethyl trinitrobutyrate, a suicient quantity being used to fill recess 17 4and form a thin layer over the top of plug 15. The detonator assembly is `completed by placing a base explosive 20such as pentaerythritol tetranitrate, a'bove cast intermediate explosive 19 and compressing the assembly using a pressure of at least 10,000 p.s.i. f

Obviously many modifications and variations of the present invention are possible in the light of the above teachings. It is therefore to be understood that within the scope of the appended claims the invention may be practiced otherwise than as specifically described.

What is claimed as new and desired to be secured by Letters Patent of the United States is: l

l. An electrical detonator comprising a cylindrical casing having a bore formed axially therein, a second bore of less diameter than the rst named bore formed in an end portion of said casing to provide an annular shoulder therebetween, a ceramic plug disposed within said first named bore in abutting engagement with said shoulder, a pair of metallic electrodesmolded within said plug in mutually spaced relation, one end of each of said electrodes projecting beyond said casing and the other end thereof being iiush with the end of saidplug, a fine bridge wire interconnecting said electrodes at the inner end surface of said plug, a coating of spray metal securing the bridge Wire to said electrodes, said spray metal being applied to the end of the plug in a manner to form a narrow diametrical slot transverse to said bridge wire and a thin annular portion -about the periphery thereof in communication with said slot in a manner `whereby the bottom portions of said slot and annular portion are free of spray metal,` a quantity of `finely divided explosive powder disposed within said slot in intimate contact with said bridge wire4 and sutiicient to fill the slot, a

second cylindrical plug of ceramic material of a diam` intermediate explosive being cast in place and in contact with said ignition charge, and a base charge arranged within said first named bore and tightly pressed into contact with said intermediate charge.

2. A detonator according to claim 1 in which said ignition charge is composed of nely divided pentaerythritol tetranitrate.

3. A detonator according to claim 1 in which the intermediate explosive charge is composed of trinitroethyl trinitrobutyrate'.

4. A detonator according to claim 1 in which the base explosive is composed of pentaerythrito'l tetranitrate.

5. A detonator according to claim 4 in which the base explosive is compressed Within the casing at a pressure of at least 10,000 pounds per square inch.

6. A detonator according to claim 1 in which the electrodes are provided with a coating of tin prior to the application of spray metal thereto.

7. A detonator according to claim l in which the casing is composed of brass.

8. A detonator according to claim 1 in which said plugs are composed of glass.

9. A detonator according to claim 1 in which the diameter of said bridge wire does not exceed .005 inch.

l0. A detonator according to claim 1 in which the width of said slot does not exceed .05 inch.

11. A detonator according to claim 1 in which said casing is composed of material having an acoustical impedance of higher value than the acoustical impedance of said explosive.

References Cited in the le of this patent UNITED STATES PATENTS 

